/*
 * Copyright 2009 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.pennychecker.eventbus;

public abstract class Event<H extends EventHandler> {
	/**
	 * Type class used to register events with the {@link HandlerManager}.
	 * <p>
	 * Type is parameterized by the handler type in order to make the addHandler
	 * method type safe.
	 * </p>
	 * 
	 * @param <H>
	 *            handler type
	 */
	public static class Type<H> {

		private static int nextHashCode;
		private final int index;

		/**
		 * Constructor.
		 */
		public Type() {
			index = ++nextHashCode;
		}

		// We override hash code to make it as efficient as possible.
		@Override
		public final int hashCode() {
			return index;
		}

		@Override
		public String toString() {
			return "Event type";
		}
	}

	private boolean dead;
	private Object source;

	/**
	 * Constructor.
	 */
	protected Event() {
	}

	/**
	 * Returns the type used to register this event. Used by handler manager to
	 * dispatch events to the correct handlers.
	 * 
	 * @return the type
	 */
	public abstract Type<H> getAssociatedType();

	/**
	 * Returns the source that last fired this event.
	 * 
	 * @return object representing the source of this event
	 */
	public Object getSource() {
		assertLive();
		return source;
	}

	/**
	 * This is a method used primarily for debugging. It gives a string
	 * representation of the event details. This does not override the toString
	 * method because the compiler cannot always optimize toString out
	 * correctly. Event types should override as desired.
	 * 
	 * @return a string representing the event's specifics.
	 */
	public String toDebugString() {
		String name = this.getClass().getName();
		name = name.substring(name.lastIndexOf(".") + 1);
		return "event: " + name + ":";
	}

	/**
	 * The toString() for abstract event is overridden to avoid accidently
	 * including class literals in the the compiled output. Use {@link GwtEvent}
	 * #toDebugString to get more information about the event.
	 */
	@Override
	public String toString() {
		return "An event type";
	}

	/**
	 * Asserts that the event still should be accessed. All events are
	 * considered to be "dead" after their original handler manager finishes
	 * firing them. An event can be revived by calling {@link GwtEvent#revive()}
	 * .
	 */
	protected void assertLive() {
		assert (!dead) : "This event has already finished being processed by its original handler manager, so you can no longer access it";
	}

	/**
	 * Should only be called by {@link HandlerManager}. In other words, do not
	 * use or call.
	 * 
	 * @param handler
	 *            handler
	 */
	protected abstract void dispatch(H handler);

	/**
	 * Is the event current live?
	 * 
	 * @return whether the event is live
	 */
	protected final boolean isLive() {
		return !dead;
	}

	/**
	 * Kill the event. After the event has been killed, users cannot really on
	 * its values or functions being available.
	 */
	protected void kill() {
		dead = true;
		source = null;
	}

	/**
	 * Revives the event. Used when recycling event instances.
	 */
	protected void revive() {
		dead = false;
		source = null;
	}

	/**
	 * Set the source that triggered this event.
	 * 
	 * @param source
	 *            the source of this event, should only be set by a
	 *            {@link HandlerManager}
	 */
	void setSource(Object source) {
		this.source = source;
	}
}
